The present invention relates to new organostannic stabilizers for vinyl halide resins and their method of preparation.
The new organostannic stabilizers are of the formula: ##STR1## in which R.sub.1 ' is the radical of an olefin compound containing a carbonyl group adjacent to the carbon-carbon double bond. Such olefin compounds are of the formula: ##STR2## in which R.sub.2, R.sub.3, R.sub.4 represent hydrogen or an alkyl hydrocarbon radical containing 1 to 3 carbon atoms and R.sub.1 is an alkyl group, a hydroxyl or a hydrocarbon group containing oxygen.
These olefine compounds include methyl, ethyl, or hexyl acrylate, acrylic acid, vinyl methyl ketone, and methyl crotonate. The group ##STR3## is the radical of mercapto alkyl ester in which the mercapto group is contained in the alcohol radical of the ester, R.sub.6 being an alkyl containing 1 to 18 carbon atoms; it may belong to any aliphatic mono- or di-acid; however, the preferred esters are derived from fatty acids, in particular caprylic, pelargonic, capric, undeconoic, lauric, myristic, palmitic, stearic acid and isostearic acid or mixtures of such acids.
"n" may be equal to 2, 3 or 4; one of the CH.sub.2 's may be substituted by a hydroxyl group.
These new organostannic stabilizers ##STR4## are obtained by the reaction of organostannic trihalides R.sub.1 'SnHal.sub.3 and mercaptoalkyl esters ##STR5## that is to say esters in which the mercapto group is present in the alkyl radical of the ester and not in the acid radical, as in the case of certain products described in the prior art. It is surprising to note that due to this difference in the position of the --SH group, the activity of the new organostannic esters is imparted with remarkable effectiveness. In addition, there are the advantages of ease of preparation and of purification of the substances.
The stannic trihalides themselves can be obtained either in accordance with the process described in French Pat. No. 2,285,392 or, preferably, in accordance with the process described in the French Patent Application filed on this date by the Societe Nationale Elf Aquitaine, by the action of a stannous compound on an excess of an olefin compound of formula (1) in the presence of a hydracid, the mixture being free of solvent.
These new organostannic compounds have excellent properties for the stabilization of the vinyl halide resins, particularly polyvinylchloride; they make it possible to reduce the discoloration of the vinyl halide resins during heating, without interfering with control of viscosity.
They may be used either alone or in combination with the other stannic stabilizers known from the prior art; in particular, they give excellent results in combination with the dialkyl tins such as, for instance, di-n-butyl tin bis(isooctylmercaptoacetate) Bu.sub.2 Sn(SCH.sub.2 CO.sub.2 i.C.sub.8 H.sub.17).sub.2 in proportions varying between 5 and 95% of monoalkyl tin to 95 to 5% of dialkyl tin.
The resins which contain a halogen to which the invention applies may be homopolymers, such as polyvinylchloride, polyvinylidene chloride, polychlorotrifluoroethylene, polytetrafluoroethylene, polychloroether, polydichlorostyrene, etc., copolymers such as polyvinylchlorides modified by methylene and/or propylene, by acrylonitrile butadiene styrene, ethylene vinyl acetate and the like.
The new stabilizers may be incorporated in the resin after the polymerization but before the drying of the polymer or else at the time of the use of the latter; their proportion may vary within wide limits, in particular from 0.1 to 5% of the weight of the resin, and particularly from 0.5 to 2%.